When the heart is paced in the left ventricle (LV), there may be unwanted stimulation of the phrenic nerve that causes contraction of the diaphragm. The left phrenic nerve descends on the pericardium to penetrate the left part of the diaphragm, and in most people, the left phrenic nerve runs close to the lateral vein. In the clinic, the pacing configuration or the stimulation parameters may be modified in an effort to avoid phrenic nerve stimulation. Examples of pacing configurations include LV bipolar, LV to can, LV to RV (right ventricle) also referred to as “extended bipolar”; and examples of stimulation parameters include the amplitude (e.g. voltage) and pulse width. The anatomic location of the phrenic nerve varies within patients. Additionally, the veins are not always in the same location with respect to the ventricle and the nearby passing nerve. Also, the selected vein in which to place the lead may vary.
Unintended phrenic nerve activation (an unintended action potential propagated in the phrenic nerve) is a well-known consequence of left ventricular pacing. The unintended phrenic nerve activation may cause the diaphragm to undesirably contract. Unintended phrenic nerve activation may feel like hiccups to the patient. Unintended phrenic nerve activation can occur when the electric field of the LV pacing lead is proximate to the left phrenic nerve and is at a stimulation output that is strong enough to capture the nerve. As a consequence, unintended capture of the phrenic nerve may require modification of the strategy for implanting the pacing lead. For example, the LV pacing electrodes may not be positioned in a preferred position to capture the LV for a pacing therapy such as CRT, or the clinician may decide not to implant an LV pacing electrode but rather rely on other pacing algorithms that do not pace the LV. A special office visit after implant may be necessary or desirable to reprogram the device to avoid phrenic nerve stimulation. Further, although phrenic nerve stimulation is commonly assessed at implant, unintended phrenic nerve activation caused by phrenic nerve capture during pacing can appear post-implant for a variety of reasons such as reverse remodeling of the heart, lead micro-dislodgement, changes in posture, and the like.